When turning the engine off on a machine, it is desirable to ensure that no pressure is trapped in any of the actuators. This is very important when it is desirable to change the implement/work tool. Some implements have actuators or motors located thereon and fluid is provided thereto through quick disconnect hydraulic lines. In previous hydraulic systems, the operator was able to mechanically move the main control valve to each of the operative positions with the engine shut down, thus venting any fluid trapped in the associated actuator or motor. In previous electro-hydraulic systems having electro-hydraulic controls associated with the directional control valves, movements of the directional control lever does not permit operation of the directional control valve. This is true since the electrical control merely moves a hydraulic pilot valve which directs pressurized fluid from a source of pressurized fluid to move the main directional control valve. With the engine shut down, there is no power to operate the source of pressurized fluid. Consequently, there is no pressurized fluid to move the main control valve. Such an arrangement is shown in U.S. Pat. No. 5, 138, 838 which issued on Aug. 18, 1992 and assigned to Caterpillar Inc.
The present invention is directed to overcoming one or more of the problems as set forth above.